The present invention relates to a pivotable suction tube for taking up a yarn from a bobbin and transferring the yarn to an operating element. The pivotal suction tube has a longitudinally extending slot on its side towards the bobbin.
For automatic start-up, it is known to provide on open-end spinning machines, for automatic take-up of the yarn from a bobbin, a suction tube which can be pivoted into the immediate neighborhood of the bobbin. The suction tube has an elongated slot on its side towards the bobbin so that a section of the yarn sucked into the suction tube leaves again through the elongate slot in the manner of a chord, so that it is accessible to operating elements which take part in the start-up and can be grasped by them (DE-OS No. 2,008,142). However, this slot has the disadvantage that a very large reduced pressure must be produced because of the great loss of reduced pressure through the slot, so that the yarn is taken up with certainty from the bobbin and sucked into the suction tube. A powerful source of reduced pressure with high power usage is thus required.
To avoid this disadvantage, it is already known to construct a suction tube without a slot (DE-OS No. 2,620,805). In order, nevertheless, to make the yarn accessible here and to be able to transfer it to an operating element, the suction tube requires a large pivoting path. In spite of this, however, it is not possible, with pivoting paths realizable in practice, to feed the yarn in this pivoting motion to an operating element, since the distance from the mouth of the suction tube to the operating element located in the vicinity of the spinning element is very large. Therefore, a gripper is required which grips the yarn and feeds it to the operating element while maintaining the yarn tension. Because of the large pivoting regions of the suction tube and also of the gripper, the prior art apparatus is extremely expensive. In addition to this, a relatively large lapse of time is necessary because of the additional pivoting path of the suction nozzle and also because of the gripping of the yarn and its feeding to the operating element.